1. Field of the Invention
The present invention relates to an image forming apparatus having the function of images formation on a recording material, and a conveying device for conveying a sheet material, which is provided for such apparatus.
2. Related Background Art
In the conventional ink jet recording apparatus (FIG. 14), a sheet material is fed from a sheet feeding portion 2 to a conveying portion 3 one by one, and conveyed to a position that faces a recording head 7. The recording head 7 performs ink jet recording on the sheet material P, which is mounted on a carriage reciprocating in the direction orthogonal to the conveying direction of the sheet material P. When the sheet material P is conveyed to the position facing the recording head 7, the recording head 7 discharges ink in accordance with recording information transmitted from a personal computer or the like, which is arranged externally, thus performing recording on the sheet material P placed on a platen 34.
Then, the structure is arranged so that the sheet P on which recording has been completed is expelled by use of an expeller roller 41 and a spur 42, which is a rotational body in point contact with the sheet P, arranged for the sheet expelling portion 4, thus conveying the sheet material to the expelled-sheet tray 70, which is installed on the downstream side of the recording apparatus, and stack it thereon.
In this conventional ink jet recording apparatus, however, when a sheet material P is expelled after recording and stacked on the expelled-sheet tray 70, the recorded image on the sheet material P, which has been already stacked on the expelled-sheet tray 70, may be disturbed by rubbing of sheet materials P themselves if ink on the recorded surface of such preceding sheet material p is yet to be dried.
Now, therefore, there is a device made available for retaining sheet materials in the expelled-sheet stacker arranged on the downstream of the expeller roller pair 41 and 42, which uses elongated guide members, as shown in FIGS. 15A and 15B, for example. Here, as shown in FIG. 15A, recording is made on the sheet material 114, while being held by the guide members 131. Then, with the completion of recording, the guide members 131 are released (FIG. 15B) so that the sheet material is stored on the expeller stacker 130. With this device, it is possible to deal with the aforesaid problem more reliably.
The arrangement of this device, however, makes the recording apparatus itself very large inevitably, and when dealing with sheets in various sizes, the sheet edge guide members of the sheet stacker should be made movable in the direction at right angles to the sheet conveying direction. As a result, there are problems yet to be solved, such as increased costs and slower recording speed, among some others.
With a view to solving these problems, there is a device that uses an expelled-sheet support 160 on the downstream of the expeller roller pair 41 and 42, which can be protruded in the sheet conveying direction as disclosed in the specification of Japanese Patent Application Laid-Open No. 11-268359, for example. FIG. 16 and FIG. 17 are views that illustrate the operation of the expelled-sheet support 160.
The expelled-sheet support 160 is arranged in a plural number in the widthwise direction of conveyance orthogonal to the conveying direction, and protruded as shown in FIG. 16 when the leading end of a sheet material P, which has been expelled in the horizontal direction, passes the expeller roller pair 41 and 42. Here, the sheet material P is expelled, while being supported by the expelled-sheet support 160 more in the upward direction than the horizontal, and held in the air until the leading end of the sheet material P hangs down and contacts with the expelled-sheet tray 70. After that, when the trailing end of the sheet material P passes the expeller roller pair 41 and 42, it is drawn in the direction opposite to the sheet conveying direction, and the sheet material P is stacked on the expelled-sheet tray 70 as shown in FIG. 17.
In this way, it is made possible to solve the aforesaid problems, while dealing with the recording performance on sheet in various sizes, without making the recording apparatus itself larger. Nevertheless, since a sheet material P is supported by the expelled-sheet support 160 more in the upward direction than the horizontal, there may be some cases where adverse effect is produced on the recording quality, because it is ideal for a recording apparatus that the passage of a sheet material P is horizontal.
Also, depending on the kinds of sheet material P, such as a thick specially treated sheet capable of performing high quality recording thereon, for example, there is almost no problem that ink yet to be fixed is rubbed immediately after recording as described above. By the utilization of this property, it is possible to maintain high-quality recording when recording is made on a specially treated paper or the like without the protrusion of the expelled-sheet support 160 or some other measures.
In recent years, however, the kinds of specially treated sheet dedicated to use for ink jet recording have become various, and materials used for the layers that form such sheet material are also different. As a result, the behavior of a sheet material immediately after recording is various depending on the thickness, firmness, degree of ink absorption, and only the protruding and retraction operation of the expelled-sheet support 160 is no longer good enough for dealing with each of the sheet materials P appropriately.
Particularly, in recent years, an ink jet recording apparatus is made to perform high-speed recording along with the advancement of the manufacturing technologies and techniques of an ink jet recording head, which makes the provision of multiple nozzle possible, with the advancement of the ink jet recording technologies and techniques, which makes it possible to deal with high-frequency discharge signals, and along with the high-speed processing of recording data, which is made possible by the availability of inexpensive storage device. As a result, recording time per sheet becomes shorter, and the tendency is that the next sheet material is expelled in a state where most of ink immediately after recording is yet to be fixed, thus making it easier for ink rubbing to occur. Also, it is assumed that the ink material, which is not easy to be dried, is even adopted for an ink jet recording apparatus for recording images in high-density with high coloring. Therefore, it is prerequisite more than ever that measures be taken to solve the aforesaid problems.
It is an object of the present invention to provide a sheet conveying device capable of preventing image quality from being degraded due to rubbing of ink yet to be fixed on the sheet material that has been expelled last by a sheet material being expelled following it, and also, to provide an image forming apparatus provided with such device.
It is another object of the invention to provide a sheet conveying device capable of forming an optimal curve for a sheet material in accordance with the size, material, thickness, and others of the sheet material in order to prevent image quality from being degraded due to rubbing of ink yet to be fixed on the sheet material that has been expelled last by a sheet material being expelled following it, and also, to provide an image formatting apparatus provided with such device.
It is still another object of the invention to provide a sheet conveying device, which comprises a conveying mechanism for conveying a sheet material almost horizontally; and a supporting member movably attached to the conveying mechanism for supporting a sheet material, at least two or more supporting members being provided as aforesaid supporting member in the widthwise direction of conveyance substantially orthogonal to the conveying direction of sheet material, and at least one or more of the aforesaid supporting members being capable of supporting a sheet material in positions having different heights in the direction substantially perpendicular to the sheet material, and further, the positions of the aforesaid supporting members for supporting a sheet material being variable substantially in the same direction as the conveying direction of sheet material, and also, to provide an image forming apparatus provided with such device.